I accidentally doubled the ricotta in this recipe. Is it ruined?

No it's not ruined. It will just be "cheesier". Depending on the ricotta, you may end up with extra liquid being produced, and threaten you with a soupy lasagna. No sweat- just check it part way through the baking, and pour off any extra liquid. If you are of a mind to, you can save that back for making soup with. Freeze it until wanted.

Hayley...Not at all. The dish will just be a little bit richer for the extra ricotta.
If it's all mixed in, just bake as planned, or maybe a few extra minutes to account for the extra pound of cheese.
And taste it yourself after baking and resting a few minutes and before serving. It may need a bit more salt, pepper and/or some nutmeg, again to account for the extra cheese.
Happy Christmas and enjoy your day!